The CHALLENGE of quantifying impacts of IMTA on the environment

Integrated Multi-Trophic Aquaculture (IMTA) promotes a new circular economy model since it is based on an efficient reuse of resources, including waste, in traditional aquaculture facilities. Farmers combine fed species with other organisms that capture their sustenance from the farming environment in an integrated waste-recycling marine polyculture system (Fig. 1). 

Fig. 1 – Schematic explanation of IMTA. Excess nutrients from fish farming can be used to cultivate other species of high commercial value

To be able to predict responses of a production system it is important to count with mathematical models that replicate the fluxes within the productive compartments of the system. However, there are a multitude of IMTA systems that can be developed either in marine or fresh water, in open water or land based. Fig. 2 characterizes the different systems within the INTEGRATE project that were considered for modelling. Conceptual models are normally used to reduce the complexity of these systems. On the one hand, it is unrealistic to develop just one model to represent all IMTA systems even if the biological processes are similar; on the other hand, it is impracticable to have one model for each of them.

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Fig. 2 – Flowcharts from INTEGRATE case studies: (a) Case study 1 (NUIG/ISC): Carnivore – Macroalgae/Carnivore – Omnivore; (b) Case study 2 (CEVA/ALGA+): Filter feeders – Detritivore – Macroalgae; (c) Case study 3.1(ALGA+):  Carnivore + Omnivore polyculture – Macroalgae; (d) Case study 3.2 (CTAQUA): Carnivore monoculture – Filter feeder – Macroalgae; (e) Case study 3.3 (IPMA): Carnivore + Omnivore + Detritivore polyculture – Filter feeder – Macroalgae.

To summarize the different IMTA systems implemented in the INTEGRATE project (please see our previous newsletter #6 for details of the case studies) a conceptual compartment model was developed for land-based semi-extensive IMTA in ponds that accommodate 5 trophic compartments (carnivores – detritivores – filter feeders – phytoplankton – macroalgae) and displays their structural organization and functioning (Fig. 3).

Fig 3 – General overview of the biogeochemical state variables and fluxes within the conceptual pond IMTA model. Square boxes represent functional groups defined in the model. Arrows indicate fluxes of energy, carbon and inorganic nutrients: red – inputs; green – outputs; blue – internal fluxes.

This conceptual compartment model, developed using the Stella software, will allow us to obtain a list of parameters and data. These will be assessed in order to provide a prediction of the environmental performance of IMTA through a Life Cycle Assessment (LCA), which our project partners from IPMA, Portugal, are working on at the moment.